AB0671 HISTOPATHOLOGICAL, CLINICAL AND SEROLOGICAL FEATURES IN IIM PATIENTS FROM A SINGLE CENTER COHORT
Authors: T. Vojinovic, M. Olivari, M. Fredi, F. Franceschini, I. Cavazzana
Journal: Annals of the Rheumatic Diseases (2022)

Background Idiopathic inflammatory myositis (IIM) is a group of heterogeneous autoimmune diseases, characterized by myositis-specific (MSA) or myositis-associated autoantibodies (MAA). Muscle biopsy is the diagnostic gold standard, but correlations with elevated creatine level (CK) or MSA/MAA are unclear. Objectives To evaluate the association between specific histological findings and clinical and/or serological features in IIM patients from a single tertiary Rheumatology referral center. Methods We retrospectively analyzed demographic and clinical data from medical charts, of 184 patients affected by IIM followed-up for &gt;1 year. Muscle biopsies of 89 IIM patients were retrieved from deltoid, biceps or quadriceps muscle, snap-frozen and stored at -80°C and processed for routine histology and histochemistry. Results The majority of our muscle biopsy cohort was represented by Dermatomyositis (DM) (39.3%), Polymyositis (PM) (29.2%) and Anti-synthetase syndrome (ASS) (13.5%), whereas the rest was composed of Overlap Syndrome (OS), Immune-Mediated Necrotizing Myopathy (IMNM) and Inclusion-Body Myositis (IMB) (13.5%, 2.2% and 2.2% respectively). DM presented perifascicular atrophy in 85% of cases and perivascular and perifascicular infiltration in only 40% of cases, similar to other types of IIMs. The overall histology finding was characterized by minimal inflammation and/or necrosis but major atrophy. In comparison, Polymyositis showed more endomysial infiltration and necrosis (Table 1). ASS was characterized by atrophy and perifascicular necrosis in 83% of cases, with perimysial and perivascular infiltration in 67% of cases. Those characteristics were observed both in anti-Jo-1+ (13.9%) as well as non-Jo-1+ ASS patients (13.2%). Non-Jo-1+ ASS patients presented endomysial infiltration, invading or enveloping the muscle fibers (not present in anti Jo-1+) (p: 0.036), with addition of rimmed vacuoles and aspecific clinical presentation. Moreover, in DM, anti-Mi2+ antibodies (9.3%) were significantly associated with perifascicular regeneration and endomysial infiltration, in comparison to both anti-TIF1γ+ (5.8%) and anti-NXP2+ patients (4.6%). No significant histopathological features were found in patients with anti-Ro52 autoantibodies (37.2%), that represented the most frequent MAA in our cohort. Table 1. BIOPSY CHARACTERISTICS ASS 12 (%) PM 35 (%) DM 26 (%) p [OR] ASS vs PM p [OR] PM vs DM diffuse atrophy 3 (25) 34 (97.1) 8 (30.8) &lt;0.0001 [0.010 (0.001-0.106)] &lt;0.0001 [76.5 (8.8-660.6)] perifascicolar degeneration ---- 29 (82.9) 15 (57.7) ---- 0.044 [3.544 (1.09-11.5)] prevalent necrosis ---- 10 (28.6) 1 (3.8) ---- 0.017 [10 (1.19-84)] Jo1 12 (% ) PL7/PL12 5 (% ) p [OR] endomysial infiltration (invading fibers) 0 3 (60) 0.015 [inf] Mi2 8 (% ) TIF1γ 5 (% ) NXP2 4 (% ) p [OR] Mi2 vs TIF1γ p [OR] Mi2 vs NXP2 perifascicolar regeneration 8 (100) 1 (20) 0 0.007 [inf] 0.002 [inf] endomysial infiltrate (surrounding fibers) 6 (75) ---- 0 ---- 0.061 Conclusion No significant associations emerged between CK levels, different types of IIM and MSA. Some histological features seem to define subtypes of DM. A precise definition of autoantibody profile in IIM could define not only a clinical phenotype but also the muscle damage distribution. Disclosure of Interests None declared